# On the concordance of cosmological data in the case of the generalized Chaplygin gas

## TL;DR

This paper examines whether various cosmological data sets are consistent within the generalized Chaplygin gas model, which unifies dark matter and dark energy, and finds they only agree near the standard LCDM model.

## Contribution

It provides a comparative analysis of multiple cosmological data sets within the generalized Chaplygin gas framework, assessing their concordance.

## Key findings

- Data sets only overlap for models close to LCDM
- BOSS Lyman alpha forest BAO measurements are significant
- Concordance is limited to models near alpha=0

## Abstract

The generalized Chaplygin gas cosmology provides a prime example for the class of unified dark matter models, which substitute the two dark components of the standard cosmological LCDM concordance model by a single dark component. The equation of state of the generalized Chaplygin gas is characterised by a parameter alpha such that the standard LCDM model is recovered in the case alpha=0 with respect to the background dynamics and the cosmic microwave background (CMB) statistics. This allows to investigate the concordance of different cosmological data sets with respect to alpha. We compare the supernova data of the Supernova Cosmology Project, the data of the baryon oscillation spectroscopic survey (BOSS) of the third Sloan digital sky survey (SDSS-III) and the CMB data of the Planck 2015 data release. The importance of the BOSS Lyman alpha forest BAO measurements is investigated. It is found that these data sets possess a common overlap of the confidence domains only for Chaplygin gas cosmologies very close to the LCDM model.